Metal pnictogenide films have attracted considerable attention due to their many desirable properties. Metal pnictogenides such as titanium nitride, zirconium nitride and hafnium nitride exhibit metallic behavior, extreme hardness, high melting point (ca 3000.degree. C.), chemical resistance to organic solvents and inorganic acids to the point of inertness, and low temperature super conductivity. As a result, metal pnictogenide films are suitable for many applications. Well known examples include wear resistant, friction reducing coatings for machine tools and gold colored decorative coatings.
In addition, the optical properties of metal pnictogenides make them suitable for use as wave length-selective transparent optical films and solar control coatings for windows. In microelectronic devices, metal pnictogenide films are of use as low resistance contacts and diffusion barriers that interconnect metallization schemes. See Fix et al. Chemical Vapor Deposition of Titanium, Zirconium, and Hafnium Nitride Films, CHEM. MATERIALS, (1991), 3, pp. 1138-1148, herein incorporated by reference.
Metal pnictogenide films have been prepared by chemical vapor deposition techniques (CVD) and physical vapor deposition (PVD) techniques such as sputtering and reactive evaporation. However, these prior art processes fail to consistently provide high quality films exhibiting low resistivity, low levels of contamination from other elements and highly reflective gold colored films. In addition, most of these prior art CVD processes require the use of an excess of vaporous ammonia in combination with either a metal halide or a metal dialkylamide.
The deposition of titanium nitride films from the reaction of vaporous titanium tetrachloride and vaporous ammonia has been explored in a variety of reaction conditions. For example see Y. Saeki et al., Reaction Process Of Titanium Tetrachloride With Ammonium And The Vapor Phase And Properties Of The Titanium Nitride Formed, BULL. OF THE CHEM. SOC. OF JPN., (1982), 55, pp. 3193-3196; A. Aguero et al., A Low Temperature CVD Process For Tin Coatings, MAT. RES. SOC. SYMP. PROC., (1989), 168, pp. 311-316; and S. R. Kurtz and R. Gordon, Chemical Vapor Deposition Of Titanium Nitride At Low Temperatures, THIN FILMS, (1986), 140, pp. 277-290. These references are herein incorporated by reference.
However, these prior art processes fail to produce the desired high quality titanium nitride films. In particular, films produced by these prior art processes lack the characteristic highly reflective gold color, the desired one to one stoichiometry, and are contaminated with significant amounts of carbon and chlorine.
Metal pnictogenide films of titanium, zirconium and hafnium have also been produced using a multi-reactant feed stream of vaporous ammonia and vaporous tetrakis (dialkylamido) metal (IV) complexes. However, although the titanium nitride film produced by this process possessed the requisite highly reflective gold colored appearance, high purity films were obtained only at deposition temperatures of approximately 200.degree. C. Increasing deposition temperature resulted in increased contamination. Also, the titanium nitride films produced by this process possessed slightly nitrogen rich stoichiometry.
These prior art processes are also handicapped due to an extreme vulnerability to fluctuations in certain experimental parameters. Kurtz and Gordon reported that deposition of high quality TiN films was dependent upon careful control of the vaporous reactant mixing conditions. Failure to exercise this `careful control` resulted in the formation of powder. See, Kurtz et al., CVD Of TiN At Low Temperatures, THIN Solid FILMS, (1986), 140, pp. 277-290. Other experimental variables having a significant impact upon the successful CVD of metal pnictogenide films using multi reactant feed streams are the gas flow rates, pressure, reactant concentration and deposition temperature.
In addition to these practical difficulties, these multiple reactant CVD processes are undesirable because of the excess ammonia required. Due to ammonia's toxicity and hazardous handling properties, its presence in a commercial process is highly undesirable. While at least one prior art reference discloses the production of metal pnictogenide films using metal chloride and excess primary and secondary amines, the substitution of ammonia with an excess of selected primary and secondary amines in no way addresses the practical difficulties of using such compounds in a commercial industrial process.
As a result of the deficiencies of the prior art processes, CVD processes employing a single reactant stream for the production of metal pnictogenide films are desirable. While some single sources for metal pnictogenide films have been reported, they fail to produce the desired high quality metal pnictogenide films.
For example, in two prior art references, Fix et al. Synthesis of Thin Films By Atmospheric Pressure Chemical Vapor Deposition Using Amido And Imido Titanium (IV) Compounds As Precursors, CHEM. MATER., (1990), 3, pp. 235-241 and Sugiyama et al. Low Temperature Deposition Of Metal Nitride By Thermal Decomposition Of Organo Metallic Compounds, J. ELECTRO. CHEM. ASSOC.: SOLID STATE SCIENCE AND TECHNOLOGY, (November 1975), 122, pp. 1545-1549, the use of metal tetrakis (dialkylamides) are disclosed as single source precursors for metal pnictogenide films. These references, which are herein incorporated by reference, indicate that the resultant films suffer from significant oxygen and carbon contamination and appear to lack the desirable mirror-like golden appearance. Both references also indicate that no film is produced at deposition temperatures less than 350.degree. C.
Accordingly, then what is desired is a single source precursor for use in CVD reactors which will produce metal pnictogenide films, particularly titanium nitride films, which are gold colored and possess high reflectivity, negligible contamination from other atomic species such as carbon, oxygen or chlorine, and low resistivity. Suitable metal pnictogenide single sources will produce a film having the desired stoichiometry, be volatile at temperatures less than 100.degree. C. and cleanly decompose to the desired product.